How Hurricanes are Formed
Hurricanes develop from belts of low pressure called easterly waves. These regions of low pressure occur in ocean winds called trade winds. On certain occasions, the easterly waves form into tropical depressions, which are characterized by a group of thunderstorms with cyclonic winds of up to thirty one miles per hour. The next stage in development is a tropical storm, with winds of up to seventy three miles per hour. Any wind speed higher than that and it is a hurricane.
The fuel that powers hurricanes is derived from latent heat from the condensing of water vapor. Thunderstorms can produce up to ten inches of rain per day, and thus produce an incredible amount of energy, up to 24 x 10นน kilowatt hours per day on average. This is the equivalent of how much power most industrialized nations use in one year (such as the United States).
Winds swirl around the eye, the calm center of the hurricane. The eye has a diameter of about twenty miles across and has very few winds or clouds. Surrounding the eye are storm clouds called wall clouds. It is within these clouds that the heaviest rains and strongest winds occur. These wind speeds are kept up by the differences in horizontal pressure between the eye and outer regions of the storm.
Initially, when a hurricane forms, its forward movement is very slow (fifteen miles per hour), but as it gets farther away from the equator, its speed increases up to sixty miles per hour in middle latitudes. But in addition to gaining speed as is moves away from the equator, it also begins to die. Eventually it looses its source of power as it passes over land and gets ripped apart by friction. Hurricanes usually only last between five and ten days.
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